Equipment and method for enhancing combustion and heat transfer in a boiler by using sound

ABSTRACT

The invention concerns equipment and a method for enhancing the combustion event and heat transfer in a heating boiler. According to the invention, the space above the major combustion zone in the combustion space of the heating boiler is equipped with sound sources, which are used to generate an acoustic field to enhance the combustion event and to achieve more complete combustion.

The invention concerns equipment and a method for enhancing the combustion event and heat transfer in a heating boiler.

The invention relates to combustion taking place in power plants, heating furnaces, heating boilers and other such combustion spaces and to enhancement of such combustion. In the following, the name of heating boiler will be used for these application objects of the invention.

Combustion is a complex event, which depends on several different factors, such as the particle size of the fuel, the combustion temperature and the structure of the heating boiler. The fuel used in the combustion event becomes oxidized, whereby heat will result. At typical combustion temperatures, combustion of hot solid matter depends on the speed at which oxygen is diffused into the surface of the matter. As the combustion proceeds, the particle size and particle mass are reduced. When burning carbon, the combustion results in carbon monoxide, which in the continued combustion will become carbon dioxide.

It is a known method to enhance the combustion event by causing turbulence to occur in the combustion space to enhance movement of the matter and heat transfer in the combustion. However, in known solutions problems still occur in the completion of combustion taking place in power plants, heating furnaces and heating boilers and other such installations. It is difficult to make turbulence generators, such as agitators, to reach high temperatures, which are typically in a range of 600-1000° C. In particular, problems occur in the combustion of non-volatile carbon particles.

Enhancing of combustion is also associated with cleaning of the heat transfer surfaces of the heating boiler to remove ash particles and unburnt carbon particles from them. Acoustic cleaning is a known cleaning method, wherein sound sources are placed in the heat transfer parts of the heating boiler and sound is produced periodically at intervals of about 2-15 minutes for a few seconds each time. Acoustic cleaning equipment is known e.g. from publications WO-82/01328 and WO-82/03803.

The purpose of the invention is to bring about equipment and a method for enhancing the combustion event in such a way that the combustion is more complete and emissions are reduced.

Another purpose of the invention is to bring about equipment of a new kind, wherein a sound source based on a pulse burner is used as the sound source.

The equipment according to the invention for enhancing the combustion event and heat transfer in a heating boiler is mainly characterised in that the space above the major combustion zone in the combustion space of the heating boiler is equipped with sound sources to generate an acoustic field in order to enhance the combustion event and to achieve a more complete combustion, and that the sound sources are placed in such a way that the acoustic pressure patterns generated by the sound sources meet at angles of 20-90° sideways and/or vertically.

The method according to the invention for its part is characterised in that in a space above the major combustion zone in the combustion space of the heating boiler a rotating acoustic field is generated by sound sources, which are located on various sides and/or at different elevations of the heating boiler.

In the arrangement according to the invention, the combustion event is enhanced in such a way in a heating boiler that an acoustic field is applied to a space above the actual major combustion zone. Matter volatilising at this location has already burnt out for the most part, but some carbon still remains in the form of small particles, which have not yet burnt The acoustic field is preferably continuous and it is generated by suitable sound sources, one or more, which are placed in the combustion space of the heating boiler. The sound source is preferably a sound source based on a pulse burner. By the arrangement according to the invention, the combustion event is enhanced in such a way that more heat is obtained from the fuel used and less combustion residue will result. At the same time, a cleaner combustion is also achieved, which means that harmful emissions are reduced.

By using the sound source according to the invention, which is based on a pulse burner, that problem is solved, which is associated with pneumatically operated sound sources in that due to the higher pressure existing inside the combustion space dust or other impurities will drift from the combustion space into the sound source. No such problem occurs in the sound source based on a pulse burner.

In the following, the invention will be described with reference to the figures shown in the appended drawing, but the intention is not to limit the invention only to the embodiments shown in the figures.

FIG. 1 shows a heating boiler and the location therein of the equipment according to the invention.

FIG. 2 shows an example of the acoustic field according to the invention.

FIG. 3A shows the sound source according to the invention.

FIG. 3B shows a valve in the sound source according to the invention.

FIG. 3C is a cross-sectional view of the sound source according to the invention.

FIG. 3D is another cross-sectional view of the sound source according to the invention.

FIG. 1 is a schematic view of a heating boiler, wherein the method according to the invention for enhancing the combustion event is applied. Sound sources S are located in combustion space 11 of heating boiler 10. The place of location of sound sources S is a space above the major combustion zone before cooling of the combustion gases. The sound sources used are preferably such sound horns known in acoustic cleaning, which produce a sound volume of 130-170 dB at a frequency of 20-1000 Hz. The sound source used may also be pneumatically operated continuous sirens or the sound source according to the invention shown in FIGS. 3A-D, which is based on a pulse burner. Due to the good penetration depth, the acoustic frequency range chosen is preferably used explicitly in order to enhance the combustion event. The power and frequency of the sound sources S may be controlled within the chosen range according to the type and size of boiler and the locations of sound sources S. The sound volume is chosen so that the acoustic pressure level generated by sound sources S is preferably no less than 130 dB at the place where acoustic pressure patterns meet, where the temperature in the combustion space 11 is typically over 800° C. Sound sources S are placed in combustion space 11 in such a way that the acoustic pressure patterns which they generate will meet at angles of 20-90° C. sideways and/or vertically.

In an advantageous embodiment of the invention, sound sources S are placed at different elevations in the heating boiler 10, and when moving upwards in the combustion space 11 the frequency of the sound source S is increased as the diameter and mass of solid particles diminish further ahead in combustion space 11. Hereby the desired effect enhancing the combustion event will remain at an optimum.

In another advantageous embodiment of the invention, sound sources S are placed in such a way in heating boiler 10 that the resulting acoustic field is rotating. FIG. 2 illustrates such a rotating acoustic field, which is generated by locating in the combustion space 11 of a heating boiler, which as regards its diameter is of a rectangular shape, four sound sources S, which are used to generate the acoustic pressure direction pattern shown in FIG. 2. A rotating acoustic field of a corresponding kind can also be generated in a heating boiler of some other shape. The number and locations of sound sources S may be different from those shown in this example, when generating a rotating acoustic field.

In an advantageous embodiment of the invention a part of the secondary and/or tertiary air needed in the combustion event is supplied through the sound sources S placed in heating boiler 10. This supplied air at the same time functions as cooling air for sound sources S.

FIG. 3A shows a sound source SP according to the invention, which is based on a pulse burner. FIG. 3B shows an example of the structure of a valve V of sound source SP, FIG. 3C is a cross-sectional view of sound source SP along line A-A′ indicated in FIG. 3A and FIG. 3D is a cross-sectional view of sound source SP along line B-B′ indicated in FIG. 3A.

The sound source used is a pulse burner, which preferably operates with the combustion reaction between a gaseous or gasified fuel and air and functions on the “pulse jet” principle known as such. In such an embodiment the sound source SP includes an antechamber SP₁, into which air under pressure is supplied through assembly L₁, a combustion chamber SP₂, into which a gaseous inflammable matter is supplied through assembly L₂, and a sound horn SP₃. Between antechamber SP₁ and combustion chamber SP₂ there is a valve/set of valves V, whose structure is shown by the cross-sectional view in FIG. 3B. In addition, sound source SP includes one or more igniters I located in combustion chamber SP₂. Combustion chamber SP₂ is surrounded by cooling devices C including cooling fins c₁, . . . , c_(n). Into cooling devices C a cooling medium, preferably cooling air or water, is conducted by way of assembly L₃.

After the combustion event, the pressure of combustion chamber SP₂ is released into the space to be cleaned, that is, into combustion space 11.

The igniting device/devices I used are preferably spark plugs or a hot shoe functioning as a constantly glowing igniting component

The pulse burner operating as sound source SP preferably uses hydrocarbon gas and air in starting. In addition, in one embodiment of the invention a gasified gas is used, which is taken from that part of the combustion space, where no secondary or tertiary air has yet been introduced.

The sound source according to the invention forms a continuous acoustic pressure pulse, with which a continuous quick pulse-like acoustic pressure can be driven into the combustion space of the boiler.

The invention may be applied in all types of power plants, heating furnaces, heating boilers and other such installations. The sound sources used are sound horns known in acoustic cleaning, but also sound sources of other kinds may be used.

The following is a presentation of the claims, but the invention is not intended to be limited only to the different embodiments presented in the claims. 

1. Equipment for enhancing the combustion event and heat transfer in a heating boiler, said equipment comprising sound sources (S) in a space above the major combustion zone in a combustion space (11) of the heating boiler (10), which sound sources (S) generate an acoustic field in order to enhance the combustion event and a more complete combustion, characterised in that the sound sources (S) are placed in such a way that the acoustic pressure patterns generated by the sound sources (S) meet at angles of 20-90° sideways and/or vertically and that the sound sources (S) are fitted into the heating boiler (10) in such a way that the generated acoustic field is rotating.
 2. Equipment as defined in claim 1, characterised in that the acoustic field generated by the sound sources (S) is continuous.
 3. Equipment as defined in claim 1 or 2, characterised in that the acoustic pressure level generated by the sound sources (S) is no less than 130 dB at the place where the acoustic pressure patterns meet.
 4. Equipment as defined in any one of claims 1-3, characterised in that the frequency of the sound generated by the sound sources (S) is in a range of 20-1000 Hz.
 5. Equipment as defined in any one of claims 1-4, characterised in that the secondary and/or tertiary air of the heating boiler (10) or a part of that air has been supplied into the boiler through the sound sources (S).
 6. Equipment as defined in any one of claims 1-5, characterised in that the sound sources (S) are fitted into the heating boiler (10) in such a way that the generated rotating acoustic field rotates in the direction of the positive acoustic pressure.
 7. Equipment as defined in any one of claims 1-6, characterised in that the sound sources (S) are fitted into the heating boiler (10) in such a way that the sound frequency increases towards the top part of the heating boiler (10).
 8. Equipment as defined in any one of claims 1-7, characterised in that the sound sources (S) are acoustic horns.
 9. Equipment as defined in any one of claims 1-7, characterised in that the sound sources (S) are pneumatically operated continuous sirens.
 10. Equipment as defined in any one of claims 1-7, characterised in that the sound sources (S) are sound sources (SP) based on a pulse burner.
 11. Equipment as defined in claim 10, characterised in that the fuel of the pulse burner (SP) functioning as sound source essentially includes a gaseous inflammable matter and an oxidiser.
 12. Equipment as defined in claim 10 or 11, characterised in that the pulse burner (SP) functioning as sound source includes an antechamber (SP₁), into which air under pressure is arranged to be supplied, a set of valves (V) opened and closed by pressure and separating the space between the antechamber (SP₁) and the combustion chamber (SP₂), and into which combustion chamber (SP₂) supply of fuel is arranged, and a sound horn (SP₃).
 13. Equipment as defined in claim 12, characterised in that a continuous supply of air under pressure is arranged into the antechamber (SP₁) of the pulse burner (SP) through an assembly (L₁).
 14. Equipment as defined in claim 12 or 13, characterised in that the supply of fuel into the combustion chamber (SP₂) of the pulse burner (SP) is arranged through an assembly (L₂).
 15. Equipment as defined in any one of claims 12-14, characterised in that the pressure of the combustion chamber (SP₂) of the pulse burner (SP) discharges into the combustion space (11) of the heating boiler (10).
 16. Method for enhancing the combustion event and heat transfer in a heating boiler, in which method an acoustic field is generated with sound sources (S) in a space above the major combustion zone in a combustion space (11) of the heating boiler (10), characterised in that a rotating acoustic field is generated by sound sources (S), which are located on various sides and/or at different elevations of the heating boiler (10) in such a way that the acoustic pressure patterns generated by the sound sources (S) meet at angles 20-90° sideways and/or vertically.
 17. Method as defined in claim 16, characterised in that sound sources (SP) based on a pulse burner are used as sound sources (S). 